Why Does Rank Tracker Show A Different Rank Then What I See In A Browser Or Elsewhere?

Rank checking is a general gauge at best.

Engines show different results to different people for different reasons for the same exact keyword/search query.  Ill talk about Google as an example just because they are the largest.

Useragents/Browsers:
You can literally take the same machine and install multiple different browsers and load google.com in each of them and search for the same exact query and get multiple different sets of search results back.  Sometimes they can vary dramatically, 1 set might have domains that another set doesn't even show, all on the same pc.

IPs:
Different IPs generally will see different sets of results, and not just for local type searches, in general.  IPs in the same state/country can show considerably different results and as you change from country to country you might be looking at 100% different results for the same query.  In Rank Tracker you always want to try and use proxies or an IP from the same country as your potential viewers would be from.

10 vs 100 and being logged in:
Even simple things like changing results from 10 results per page to 100 results per page can show dramatically different results.  Also being logged into google can show different results.

The Big Picture:
You can't know what your end user will be using in the way of browsers, how many results per page, their IP and other such factors that all affect what they see when they search.  If you take 1 rank tracking tool using 1 user agent and ip and X results per page and then look at it vs Scrapebox you can easily see a variance in your rank and yet further variance if you look at it in a browser.

The most important thing here is there is No Wrong Answer. If your browser shows 1 position for a term and your site and Rank Tracker shows another that doesn't mean either is wrong or broken, it means that google is serving up different sets of results.   If anything its helpful to see this as your customers might see what Rank Tracker sees and not what your browser sees.

You could literally take 50 people and set them up different and have all 50 people search the same thing and get 50 different sets of results back, some of which may include your results in positions all over the map and others which won't include your site at all.  This is how google works.

So its helpful to be aware that rank tracking is a loose idea of how your site and SEO/Link Building is doing over all, but its not an exact science as google is not consistent in SERPs for all people.